The invention concerns a method for reducing the escape of fuel gases from a fuel tank for liquid fuel during a filling operation performed via a filler section of the fuel tank. The invention further concerns a motor vehicle with a fuel tank which is provided with a filler section into which a filling device can be introduced for performing a filling operation.
In fuel tanks for liquid fuel, a gas phase forms above the liquid fuel. The gas pressure of this gas phase is essentially determined by the type of liquid fuel and the ambient temperature. If the fuel tank is nearly empty, it must be refilled with liquid fuel to maintain the functioning capacity of the motor vehicle. For automobiles, this is usually accomplished at gasoline stations. Upon introduction of the liquid fuel, the liquid fuel displaces gas volume from the fuel tank so that corresponding fuel gases escape from the fuel tank during refueling and pass into the environment. The person refilling the fuel tank is exposed to the fuel gases in the process. Furthermore, general air pollution by the fuel gases occurs as a result.
It is known that filling devices connected by a hose to the gasoline station tank are provided with an extraction pump which extracts fuel gases that are displaced from the fuel tank during the filling operation and routes the fuel gases back into the gasoline station tank. If oversaturation of the gas phase in the gasoline station tank occurs in the process, this results in condensation of the fuel gases into liquid fuel in the gasoline station tank. Fitting gasoline stations with such extraction devices requires relatively expensive conversion of the gasoline stations, so that a short-term solution of the problem of fuel gases escaping during the filling operation cannot be achieved.
It is therefore the problem of the present invention to make a reduction of the escape of fuel gases from a fuel tank for liquid fuel during a filling operation necessary without conversion measures on gasoline stations which can be accomplished only slowly.
Starting from this problem, according to the invention a method of the kind mentioned hereinbefore is characterized in that, by cooling of at least a portion of the fuel tank, condensation of the fuel gases is performed.
The present invention is based on the idea of conducting the fuel gases contained in the fuel tank, which during the filling operation are expelled from the volume of the fuel tank by introduction of the liquid fuel, back into the fuel tank in which the fuel gases are caused to condense by cooling of at least a portion of the fuel tank and are added as condensed fuel to the liquid fuel contained in the fuel tank.
The advantage of the invention lies in that no transport of fuel gases into a storage tank, for example gasoline station tank, from which filling of the fuel tank to be filled is performed, is necessary, but that the fuel gases remain in condensed form in the newly filled fuel tank.
Although it is possible to cool the whole fuel tank, however it is preferable, for the purpose of saving energy, to cool only the upper portion of the fuel tank, as the fuel gases come into contact with the upper portion of the fuel tank during the filling operation. Particularly, it is preferable to cool the fuel in the filler section, as the latter has a wall surface surrounding a relatively small volume and can therefore be cooled efficiently by cooling the wall of the fuel tank.
For motor vehicles which are refueled at a stationary filling apparatus, such as land and water vehicles at gasoline stations or aircraft at airport fuelling vehicles, it is particularly advantageous if cooling is performed just shortly before the refueling operation, to minimize the energy needed for cooling. To that end, the present invention could provide that the filling operation for the fuel tank is operationally contingent upon the cooling of the fuel tank to a given degree, thus ensuring the prevention of even greater quantities of fuel gases escaping into the environment during the filling operation due to an absence of cooling or insufficient cooling.
A motor vehicle may be further equipped with a switchable cooling device arranged in or on the fuel tank for cooling of at least a portion of the fuel tank to a temperature below the condensation temperature of the fuel gases.
The required cooling is achieved upon dropping below the condensation temperature at least of a preponderance of the components contained in the fuel gases.
The cooling device is appropriately designed for cooling of at least the filler section of the fuel tank. To carry out cooling just shortly before a refueling operation, the cooling device can advantageously be activated by a switch accessible from the interior of the motor vehicle.
The cooling device for the fuel tank can be formed by a heat exchanger through which a refrigerant flows and which can be arranged on the outside of the fuel tank and in heat-conducting contact with a wall of the fuel tank. In the alternative, a heat exchanger can be integrated in the fuel tank. In the latter case, the fuel tank can preferably comprise a double-walled region which is provided with connections for the refrigerant.
One embodiment of the present invention may provide for cooling of the fuel tank by its own refrigerating machine. But in vehicles which are already equipped with an air conditioning system, it is preferable to use the refrigerant from the circuit of the air conditioning system for cooling of the fuel tank, which may be accomplished, for example, by effectively switching a corresponding ancillary circuit for the refrigerant through the heat exchanger of the fuel tank.